In my co-pending, concurrently filed application entitled "Radio Communication System Using Synchronous Frequency Hopping Transmissions", there is described a method and apparatus for specifying frequencies and a frequency-hopping sequence for radio transceivers of a communication system. In certain applications, more than one such communication system may operate in a limited geographical area. Moreover, these systems may operate independent of each other and may even be separately owned. There exists a problem to prevent mutual radio frequency interference between systems operating in close proximity. SUMMARY OF THE INVENTION
In accordance with the present invention, the disclosed radio communication system automatically detects when another radio system is within range and in response thereto selects a different group of frequency-hoppoing (FH) sequences. More particularly, when the system is initially enabled on power-up or other pre-established conditions, the control module (CM) of the system listens for a particular radio frequency control signal for a predetermined time period. If the CM detects the presence of the control signal, it is interpreted that another CM is operating within range and acting as a master system with zero or more slave CMs.
If the CM does not detect the control signal, it transmit the control signal and uses a first predetermined group of sequences for communications with stations of the system and becomes a master CM. If the CM detects a control signal, it automatically selects a second, third, etc. predetermined group of sequences for communication with stations of the system. In either event, the CM signals its stations as to which group of sequences is to be utilized for system communications.
In one embodiment, the control signal consists of two frequencies and also includes a clock sync message therein for synchronizing the operation of the systems.